Leading-in wire for electrical incandescent lamps and similar devices



July 28, 1925.

S. L. HOYT LEADING-IN WIRE FOR ELECTRICAL INCANDESCENT LAMPS AND SIMILARDEVICES Filed Aug. 2. 1921 ,il liti* Patented July 28, 1925.

UNITED STATES 1,547,394 PATENT OFFICE.

SAJlIUEI.. L. HOYT, OF EAST CLEVELAND, OHIO, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

LEADING-IN WIRE FOR ELECTRICAL IN CANDESCENT LAMPS AND SIMILAR DEVICES.

Application led August 2, 1921.

To-aZZ whom. it may concern:

Be it known that I, SAMUEL L. I-IoY'r, a citizen of the United States,residing at East Cleveland, county of Cuyahoga, State of Ohio, haveinvented certain new and useful Improvements in Leading-in `Wires forElectrical Incandescent Lamps and Similar Devices, of which thefollowing is a speciication.

My invention relates to leading-in wires for incandescent lamps, vacuumtubes and other electrical devices comprising sealed glac'ss containersand more particularly to composite leading-in wires, that is, leadinginwires made up of two or more different metals.

In the accompanying drawing, Fig. 1 is I a diagram of apparatus employedin carrying out the process forming part of my invention; F ig. 2 is adrawing made from a microphotograph of a section cut lengthwise alongthe line 2 2 of Fig. 5 of a composite wire embodying my invention; Fig.3 is a drawing made from a similar microphotograph of a composite wireof the type now in general use; Fig. 4 is an enlarged diagrammatiealcross section of a composite wire embodying my invention, and Fig. 5 isan elevation of a piece of wire embodying my invention.

In the manufacture of the usual composite leading-inwire, a nickel-ironcore at't-er proper cleaning is wound with a brass ribbon and a coppersleeve is then slipped thcreover. The composite bar so prepared issubjected to a suiiiciently high temperat-ure to cause the fusion ot thebrass ribbon which fills and overflows out of the space between the coreand the sleeve. The copper' sleeve is bonded to the metal core by thebrass. However, the brass does not always bond the copperto thenickel-iron core at all peints but sometimes leaves a space betweenihesleeve and the core. This space may not be eliminated by the rolling`swaging or :die-drawing of the composite bar. lVhen the wire containingsuch a space is sealed in the glass of an evacuated envelope, the spacebecomes a pathway for the leakage of air. In many cases, the leakage isa slow process and may not be readily detected. In fact, evacuatedincandescent lamps with such imperfect leading-in wires 'may go for manydays without giving evidence of poor vacuum` Serial No. 489,388.

By means of my invention, I so unite the sleeve material to the corematerial that the possibility of an air passage existing between thesleeve and the core is practically eliminated. By means of my inventionthe sleeve material is united to the core material by a material whichunites, probably in solid solution, with both the sleeve and the corematerials to form an allo bond. The sleeve is so rmly united to the corethat, when an attempt is made to separate the two by means of a coldchisel, the core adheres to the sleeve and is cut ofi' with it without aline of cleavage appearing between the two.

More specifically, according to my invention, a copper sleeve is bondedto a core composed of iron and nickel or similar ymetal by a materialwhich readily alloys with both copper and nickel-iron or similar alloycore to form an alloy bond. For the practice of my invention I haveprovided a `continuous process which produces composite wire ready to bedie-drawn to any desired size preferably after a preliminaryheat-treating. In carrying out this process the nickel-iron core isselected of a 7 comparatively small size so that it may be used in theform of a wire. The core is cleaned and a suitable layer of bondingmaterial placed thereon preferably by electroplating. A suitable coppersleeve or layer of copper is then placed over the layer of bondingmaterial preferably by electroplating. The composite wire is then reeledup and preferably stored for a short time after which it is given apreliminary heat-treatment preparatory to die-drawing it to a sizesuitable for use. 'My experiments seein to indicate that a better bondis obtained between the core and the sleeve when the composite wire isallowed to stand for several days before die-drawing, and I prefer tofollow this practice although it is not essential and the explanation ofthe action is not clear. -What probably results is a partial diffusionof the bonding material into the nickel-iron core and into the coppersleeve. The preliminary heat-treatment properly anneals the compositewire for working as well as perfecting the bond between the bondingmaterial, the .core and the sleeve.

The composite wire embodying my invention has a core composed of analloy of iron or similar metal and a cover of copper, the percentage ofnickel or similar metal in the core being greater near the copper coverthan at the center of the core. While the nickel layermay be found inthe composite Wire alloyed with thc copper cover and the nickel-ironcore, it may be made so thin in the process that it completely alloyswith the copper cover and the nickeliron core and loses its identity.

Referring to the drawing, the nickel-iron core wire 10 is contained on areel 11 from which it is gradually fed to a cleaning means 12 in whichit is passed between pads 13 which are saturated with a' cleaning agent,such as carbon tetrachloride, contained in the reservoir 14. It is thenfed through the usual electric annealing furnace 15 in which it iselectrically heated in an atmosphere of hydrogen entering the furnacethrough the pipe 16. In addition to annealing the Wire 107 the treatmentin the furnace reduces any oxides which may be present, From the furnace15, the wire 10 is fed to a plating tank 17 in which a layer of nickelis electrolytically deposited thereon. The plating bath 18 contained inthe tank 17 consists of a nickel-ammonium sulphate solution although anysuitable nickel-plating solution may be used. A source of direct-currentelectrical energy such as the generator 19' has the positive terminalthereof connected to a pure nickel anode 20 which is suitably supportedin the plating bath 18. The negative terminal of the generator 19 isconnected to a brush 21 which contacts with the moving wire 10. Arheostat 22 or other proper regulating means is inserted in theelectrical circuit to control the rate of plating which also dependsupon the rate of feed of the wire 10, upon the strength of the platingbath 18 l and upon the amount of wire 10 exposed to the plating bath 18.An ammeter 23 is inserted in the circuit to indicate the value of thecurrent used.

From the tank 17 the wire 10 passes over the drum .24 where a sprayof-water from the jet 25 washes off any solution carried off from thebath 18. It is then fed over a drum 25 in plating tank 26 in which alayer of copper is electrolytically deposited on the layer of nickel. Acopper cyanide solution is preferably used as the plating bath 27although any suitable copper-plating solution may be used. The positiveterminal of a source of direct current energy such as the generator 28is connected to a series of pure copper anodes 29^which are suitablysupported in the plating bath 27. The negative terminal of the generator28 is connected to a brush'30 which contacts with the metal drum 31which engages the wire 10. A proper regulating means such as a rheostat32 is inserted in the electrical circuit so as to control the rate ofplating which also depends upon the rate of feed of tl1e\wire 10 andupon the strength of the plating bath 27 as well as upon the amount ofwire 10 exposed to the plating bath. An ammeter 33 is inserted in thecircuit to indicate the value of the current used.

From the plating bath 27 the wire 10 is wound upon a reel 34. It nowconsists of a nickel-iron core 35 which carriesa layer of nickel 36 anda layer of copper 37 (see Fig. 4). Each reel of wire is preferablystored for from one to two weeks. It is my belief that when the wire isallowed to stand a diffusion occurs of the nickel layer 36 into thenickel-iron core 35 and the copper layer 37 and I have found that abetter bond seems to exist between the copper layer 37 and thenickel-iron core 35 after standing than before. The composite wire isthen preferably heated and subjected to the usual die-drawingoperations.

A specific example of my invention is as follows: The nickel-iron wire10, is selected of about 70 mils diameter and passes through thecleaning pads 13. The cleaned wire then passes to the plating bath 18,which consists of a 7 per cent (grams per cubic centimeter) solution ofnickel ammonium sulphate, at the rate of 5.5 inches a minuteapproximately 6 feet of the wire 10 being exposed to the plating bath18. The current flowing in the electrical circuit supplied by thegenerator 19 is about 0.35 ampere at a pressure of 2 volts between thecathode and anode. The layer of nickel deposited is approximatelyone-fifth mil in thickness making the diameter of the Wire -10 about 70%mils. The plating bath 27 consists of a 6.75 per centsolution of coppercyanide and has exposed therein about 200 feet of the nickel-plated wire10 which is fed through the bath at the rate of 5.5 inches a minute. Thegenerator 28 supplies a current of about 25 amperes at a pressure of 2.5volts between cathode and anode. The layer 37 of copper which isdeposited upon the nickel-plated wire 10 is approximately 5 mils inthickness making the total diameter of the composite wire 10 equal about80 mils. After storing, preferably for about ten days, the compositewire is subjected to a preliminary heat-treating.

The preliminary heat-treating consists first of a low temperature annealand in my specific process I preferably subject the wire to atemperature of about 350 for ten minutes. Then I subject the wire whichis approximately 80 mils in diameter to a cold drawing operation and, intwo passes through suitable dies, the diameter is reduced to about 70mils. The wire is now preferably heated to about 800 C. and subjected toa hot swaging operation which reduces the diameter from about 70 mils toabout 50 mils in four passes through a suitable swaging machine. Thisheat-treating relieves the strains which may exist in the compositeWire, toughens the copper and assists in alloying the layer of nickelwith the nickel-iron core and the copper coating. The composite wire isnow ready to be subjected to the usualV die-drawing process until thedia-meter is that 'desired for use.

Some of the properties of one lot of composite wire embodying myinvention are as follows:

Resistance of 100 centimeters of 8 mil Wire at 0 C. is between 2.60 and3.75 ohms;

The temperature co-,eiicient of resistance is between 0.00278 and0.00374;

The linear co-eicient of expansion is between 7.0 X 10e and 8.7 X 10-8;

The specic gravity is between 8.11 and 8.32;

The tensile strength is between 72,000 and 80,600 pounds per squareinch.

Figs. 2 and 3 are taken from micro-photographs, the circular shapesthereof being delined by the borders of the microscopic field. Thesections from which these microphotographs were made were takenlongitudinally of the wires, Fig. 2 being taken from a wire madeaccording to the present invention, and Fig. 3 from a wire of the typewhich is now in general use. It will be observed that in Fig. 2 there ispractically no line of demarcation between the light colored zone at theleft and the dark colored zone at the right, while in Fig. 3 thedemarcation is quite distinct. As stated above, this difference arisesfrom the fact that an alloy bond is actually formed in the case of thepresent invention.

As stated above, I have utilized nickel as the bonding metal but it isto be understood that metals other than nickel which are known in thearts to have similar properties are to be considered as coming withinthe scope of my invention. While I have used the term nickel in theclaims as referring to the bonding material it is t0 be understood thatthis is to be interpreted to include these metals having similarproperties to nickel as Well as nickel.

lNhat I claim as new and desire to secure by Letters Patent of theUnited States, is,-

1. A composite low expansion leading-in `wire comprising a core composedof an alloy of iron and nickel, and a cover of, copper, the percentageof nickel in said core being greater near the copper cover than at thecenter of the core.

2. A composite low expansion leading-in wire comprising a. core ofnickel-iron and a cover of copper, the percentage of nickel in saidnickel-iron core being greater near the copper cover than at the centerof the core.

3. A composite 10W expansion leading-in wire comprising a center zonehaving a high percentage of iron, an intermediate zone iaving a highpercentage of nickel and an outer zone having a high percentage ofcopper. i

4. A composite low expansion leading-in wire comprising a core or'nickel-iron and a cover of copper united thereto by a nickel alloy bond.

5. A composite low expansion leading-in Wire comprising a core composedof an; alloy of iron and nickel, an intermediate zone high in nickel anda cover of copper.

6. A composite low expansion leading-in wire comprising a core ofnickel-iron, an

intermediate zone high in nickel and a cover or' copper.

7. The process of producing a composite low expansion leading-in wirewhich consist-s in electrolytically depositing a layer of nickel upon acore of nickel-iron` then electrolytically depositing a layer of copperupon the nickel-plated nickel-iron core and then causing at least a partof said nickel to alloy with said nickel-iron core and said coppercover.

8. The process of producing a composite low expansion leading-in Wirewhich consists in feeding a nickel-iron core Wire to a nickel-platingbath, electroplating a layer of nickel upon said core wire while in saidnickel-plating bath, passing said nickelplated nickel-iron Wire to acopper plating bath, electroplating a layer of copper upon said layer ofnickel while in said copperplating bath, annealing the composite wire soformed and then Working it mechanically to cause at least a part of.said nickel layer to allo with said nickel-iron core and said la er ocopper.

9. Tie process of producing a composite low expansion leading-in wirewhich consists in assembling an intermediate layer of nickel between acore metal ot nickel-iron and a cover metal of copper and thon causingat least a part of said intermediate layer of nickel to alloy with saidnickel-iron core and said copper cover.

In witness whereof I have hereunto set my hand this 28th day of July,1921.

SAMUEL L. HOYT.

